Internal gear pumps mainly comprise an enclosure in which a gear wheel pair, having the smallest possible axial and radial play, is engaged and meshed for conveying a fluid, i.e., a pressure fluid or the like. Hereby, the suction side or lower pressure side, respectively, of the inner gear pump is linked to a fluid container, and the pressure side, or high pressure side, respectively, is linked with the hydro system which needs to be supplied. The gear wheel pair is formed by a inner rotor gear wheel and by a ring gear. The inner rotor gear wheel is driven by a motor, for instance, whereby the rotor gear, due to an active gear engaging, is turning and rotating the outer ring gear. Through this rotation, the gear teeth diverge from another and clear again the tooth gaps. The resulting vacuum and the additional atmospheric pressure on the fluid surface level, in the fluid container, cause the fluid to be drawn in. The drawn in fluid fills the created tooth gap space, which generates, after continued motion, self-contained, filled chambers, and is conveyed further to the pressure side. There, the teeth again mesh and displace the fluid from the filling chambers. The meshing teeth do not allow a return flow of the fluid from the pressure side to the suction side. In addition, the high pressure section is separated from the low pressure section by sealing teeth of the sickle.
For instance, through the publication DE 34 48 252 C2 an internal gear pump using a hydraulic liquid is known in the art in which gear wheels with overlapping, cutting tip circles are being used, which guarantees surface contact of the sealing flanks of the gearing teeth. In addition, a separating sickle is positioned in the available free space, between the intersection of the tip circles. The separating sickle is, in the known internal gear pump embodiment, constructed so that both end pieces are designed identically so that a symmetrical separating sickle is achieved.
A problem with these internal gear pumps is the occurrence of cavitation. This problem can be solved through an enlargement of the inlet area, by improving the filling and the timing, and also by providing additional pump inlets. However, these measures cause, especially with automatic transmissions, disadvantages which are induced because of a resulting increase in the required installation space and the manufacturing cost. There are also other limitations present in such a transmission system utilizing internal gear pumps. These limitations also influence the embodiment of the pump so that it is difficult to optimize the internal gear pump in regard to cavitations and avoiding the noise, without here increasing the dimensions of the internal gear pump.